1. Field of the Invention
The present invention relates to a coated paper sheet. More particularly, the present invention relates to a coated paper sheet having a high gloss, an excellent receiving property for ink transferred by a gravure printing procedure and superior reproducibility of halftone dots.
2. Description of the Related Art
It is known that, as printing paper sheets for gravure printing, coated paper sheets having a substrate sheet and a coating layer formed on the substrate sheet and comprising, as a principal components, a pigment and a binder are practically employed to obtain printed images having satisfactory clarity and color density. The conventional coated paper sheets are classified into three groups in accordance with degree of gloss, namely, mat coated paper sheets having a low gloss (a 75 degree specular gloss of 20% or less), dull coated paper sheets (having a 75 degree specular gloss of more than 20% but not more than 45%, and gloss paper sheets having a high gloss (a 75 degree specular gloss of 45% or more). Particularly, in the gloss paper sheets having a high gloss, the pigment-containing coating layer thereof is formed on a substrate sheet and then calendered by a super calender, and thus the surface of the coating layer is finished with a high smoothness and a high gloss. In this case, it is known that an increase in the smoothness causes the transferring property of the gravure printing ink to the resultant high smoothness surface to decrease. Namely, while the generation of dot-misses decreases, the density of the coating layer increases and thus the coating layer exhibits a decreased absorption property of a solvent, such as toluene, of the ink. As a result, the coloring material in the toluene solvent in the ink spreads on the surface of the coating layer to cause the ink dots to blot, expand or tail and, accordingly, the dot-reproducibility of the printed images to be decreased.
To decrease the frequency of the generation of dot-misses during the gravure printing procedure, delaminated kaolin particles, which have a high smoothness, are usually used as a principal component of the pigment for the coating layer of the coated paper sheet. However, even when the delaminated kaolin particles are contained in a high content in the coating layer, the resultant coating layer exhibits a high frequency of generation of dot-misses, namely, formation of portions of the ink images on which portions the ink is not transferred, and thus the resultant coated paper sheets are unsatisfactory in practical use.
To solve the above-mentioned problems, various attempts have been made. For example, a coated paper sheet provided with a coating layer containing a pigment having a low bulk density (0.2 to 0.6 g/cm2) as disclosed in Japanese Unexamined Patent Publication No. 9-188998 and thus having an increased cushioning property is known. Also, a coated paper sheet disclosed in Japanese Unexamined Patent Publication No. 6-065,896 and provided with a coating layer containing cubical crystalline precipitated calcium carbonate particles having a BET specific surface area of 1.5 to 4.5 m2/g is known. This coated paper sheet exhibits an increased cushioning property. However, a problem such that, when the above-mentioned coated paper sheets are subjected to a high speed printing machine, the frequency of generation of dot-misses in the printed ink images is high, is known.